Generally, a spiral concentrator of this kind comprises a spiral trough mounted on an upright central column. In a conventional concentrator the profile of the trough is generally concave and slants downwardly from the outer edge of the trough towards the central column, except in a zone immediately adjacent the central column where the trough has an inner lip which slopes upwardly. This profile will in this specification be referred to as a "conventional trough profile".
It has been proposed to alter the conventional trough profile by forming a relatively narrow, separate channel immediately adjacent the central column of a spiral concentrator. Such a channel is separated from the trough proper by means of an upstanding ridge in which splitters are provided along the height of the concentrator. The splitters are intended to divert heavier and/or larger particles from the feed material being beneficiated. A disadvantage of such an arrangement is that the use of splitters not only increases the cost of the concentrator but it is also inconvenient and not cost effective to have to set and adjust the splitters from time to time. Furthermore, the narrow channel can also trap a fraction of the beneficial product being separated, which fraction is then lost, resulting in a decrease in efficiency of the concentrator.